The use of polyalpha-olefins or copolymers thereof to reduce the drag of a hydrocarbon flowing through a conduit, and hence the energy requirements for such fluid hydrocarbon transportation, is well known. These drag reducing agents or DRAs have taken various forms in the past, including slurries or dispersions of ground polymers to form free-flowing and pumpable mixtures in liquid media.
A stable DRA (drag reducing agent) suspension is generally comprised of (1) DRA polymer particles, (2) liquid carrier, and (3) suspension aids.
In general, the DRA polymer may be obtained from solution polymerization of a water-insoluble monomer or a mixture of monomers which are subsequently precipitated to form the solid polymer particles, or from bulk polymerization (i.e., polymerization with no solvent) of said monomer(s) to form polymer which is subsequently ground into particles (which grinding may tend to degrade the polymer and its drag reduction efficiency), or produced by emulsion polymerization whereby the monomer(s) are dispersed with a large quantity of surfactant in a continuous liquid carrier prior to polymerization. The subsequent emulsion polymerization produces extremely small particles of polymer from the dispersed monomer.
The liquid carrier is preferentially a non-solvent for the DRA polymer and can vary widely, including aqueous and non-aqueous liquids, e.g., water or aqueous solutions of various pH and ionic strengths, alcohols and fatty alcohols, glycols and diols, glycol ethers, glycol esters, or mixtures of these.
Suspension aids are a necessity for DRA polymer suspensions made from solution or bulk polymerization, since such polymer particles are soft and tacky and will form films, when their unaltered surfaces come in mutual contact. Many suspension aids may be employed, e.g., stearic acid and stearate salts (magnesium stearate, calcium stearate), stearamides, polyolefin homopolymers and copolymers of various densities; oxidized polyethylene (PE); polystyrene and copolymers; carbon black and graphites; micronized polyphenyl sulfide (PPS), polypropylene oxide (PPO), polyamides, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyvinyl chloride (PVC); precipitated and fumed silicas; natural or synthetic clays, and organo-clays; aluminum oxides; boric acid; magnesium, calcium and barium phosphates, sulfates, carbonates or oxides, and the like. Many such suspension aids require heating to reach maximum effectiveness in a formulation. However, heating a process stream is economically disadvantageous in commercial production.
One common solution to preventing film formation is to coat the ground polymer particles with an anti-agglomerating agent. Cryogenic grinding of the polymers to produce the particles prior to or simultaneously with coating with an anti-agglomerating agent has also been used. However, some powdered or particulate DRA slurries require special equipment for preparation, storage and injection into a conduit to ensure that the DRA is completely dissolved in the hydrocarbon stream.
Gel or solution DRAs have also been tried in the past. However, these drag reducing gels also demand specialized injection equipment, as well as pressurized delivery systems. They are also limited to a bout 10% polymer as a maximum concentration in a carrier fluid due to the high solution viscosity of these DRAs. Thus, transportation costs of the DRA is considerable, since up to about 90% of the volume is inert material.
Thus, it would be desirable if a drag reducing agent could be developed which rapidly dissolves in the flowing hydrocarbon, which could minimize or eliminate the need for special equipment for preparation and incorporation into the hydrocarbon, and which could be injected into a pipeline without any issues.